Organic EL device and its manufacture method

ABSTRACT

A TFT is formed on a substrate. TFT has first and second regions as a source and a drain, a channel region between the first and second regions, and a gate electrode. An interlayer insulating film is formed on the substrate, covering the thin film transistor. A pixel electrode disposed on the interlayer insulating film is electrically connected to the first region of TFT via a via hole formed in the interlayer insulating film. A cover film covers the edge of the pixel electrode, exposes the inner area of the pixel electrode, and covers the surface of the interlayer insulating film in the area superposed upon the channel region of the thin film transistor to shield an ultraviolet ray. An organic light emission layer and an upper electrode are disposed on and above the pixel electrode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of PCT/JP03/001892 filedon Feb. 20, 2003, the entire contents of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to an organic EL device and itsmanufacture method, and more particularly to an organic EL device havingthe structure that an organic light emission material layer and an upperelectrode are stacked above pixel electrodes connected to thin filmtransistors.

BACKGROUND ART

A display apparatus using an organic electro luminescence (organic EL)device has been paid attention recently as a thin film light weightdisplay apparatus to be replaced with cathode ray tubes (CRT) and liquidcrystal display (LCD). Studies and developments are vigorously made onan organic EL display apparatus having thin film transistors asswitching elements for driving the organic EL display apparatus, amongother display apparatuses.

FIG. 6 is a cross sectional view of an organic EL device disclosed inJapanese Patent Laid-open Publication No. 2001-133807. On a transparentsubstrate 1 whose surface is covered with a silicon oxide film, a topgate type thin film transistor 10 is formed. The thin film transistor(TFT) 10 comprises first sand second regions R1 and R2 as a source and adrain, a channel region C between the first and second regions R1 andR2, and a gate electrode G.

An intermediate connection metal 15 is formed on the first region R1 ofTFT 10, and a data line 16 is connected to the second region R2. Aninterlayer insulating film 20 is formed covering TFT 10, intermediateconnection metal 15 and data line 16. A transparent pixel electrode 25made of indium tin oxide (ITO) is formed on the interlayer insulatingfilm 20.

A cover film 26 disposed overlapping the outer periphery of the pixelelectrode 25 covers the edge of the pixel electrode 25. An organic lightemission layer 30 is formed on the pixel electrode 25 inside the coverfilm 26. The edge of the organic light emission layer 30 rides on thecover film 26. An upper electrode 35 is formed on the organic lightemission layer 30 and interlayer insulating film 20. The cover film 26prevents a short circuit between the pixel electrode 25 and upperelectrode 35.

Photosensitive resist material is used as the material of the cover film26. By using the photosensitive resist material, the cover film 26 canbe patterned by three processes; resist material coating, exposing anddevelopment. If other insulating materials are used, additionalprocesses are necessary including etching using a resist pattern andresist pattern removal. As the photosensitive resist is used as thematerial of the cover film 26, the manufacture processes can besimplified.

It is known that if the surface of an ITO film used as the anode of theorganic EL device is forcibly oxidized prior to forming the organiclight emission film, the characteristics of the organic EL device can beimproved. As the forcible oxidation method, two methods are effective,oxidation using oxygen plasma and ultraviolet radiation in an ozoneatmosphere.

If the photosensitive resist is used as the material of the cover film26 shown in FIG. 6 and the pixel electrode 25 is exposed to oxygenplasma, the cover film 26 is etched. Therefore, ultraviolet radiation inan ozone atmosphere is preferable as the forcible oxidation method forthe surface of the pixel electrode 25.

However, as an ultraviolet ray is radiated to the pixel electrode 25,the ultraviolet ray is radiated also to TFT 10. TFT 10 is damaged by theultraviolet ray and its characteristics are degraded.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an organic EL devicewhose TFT characteristics are hard to be degraded even if an ultravioletray is radiated to a pixel electrode.

According to one aspect of the present invention, there is provided anorganic EL device comprising: first and second regions as a source and adrain formed above a substrate; a thin film transistor including achannel region between the first and second regions and a gateelectrode; an interlayer insulating film disposed on the substrate,covering the thin film transistor; a pixel electrode disposed on theinterlayer insulating film and electrically connected to the firstregion of the thin film transistor via a via hole formed the interlayerinsulating film; a cover film covering an edge of the pixel electrodeand not covering an inner area of the pixel electrode; a light shieldingfilm for shielding an ultraviolet ray, the light shielding film coveringa surface of the interlayer insulating film in an area superposed uponthe channel region of the thin film transistor; an organic lightemission film disposed on the pixel electrode and containing organiclight emission material; and an upper electrode disposed on the organiclight emission layer.

According to another aspect of the present invention, there is provideda manufacture method for an organic EL device comprising steps of:forming a thin film transistor above a principal surface of a substrate,the thin film transistor including first and second regions as a sourceand a drain, a channel region between the first and second regions and agate electrode; forming an interlayer insulating film above thesubstrate, the interlayer insulating film covering the thin filmtransistor; forming a pixel electrode disposed on the interlayerinsulating film, the pixel electrode being electrically connected to thefirst region of the thin film transistor; forming a cover film coveringan edge of the pixel electrode, exposing an inner area of the pixelelectrode, and covering a surface of the interlayer insulating film inan area superposed upon the channel region of the thin film transistor;irradiating an ultraviolet ray upon the substrate from a principalsurface side of the substrate, while a surface of the pixel electrode isexposed to an oxidizing atmosphere; forming an organic light emissionfilm on the pixel electrode, the organic light emission film containingorganic light emission material; and forming an upper electrode on theorganic light emission layer.

Since an ultraviolet ray radiated to the substrate is shielded with thelight shielding film, the intensity of the ultraviolet ray reaching thechannel region of TFT is weakened. It is therefore possible to preventthe TFT characteristics from being degraded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an organic EL device according to afirst embodiment.

FIG. 2 is a plan view of the organic EL device of the first embodiment.

FIGS. 3A and 3B are cross sectional views of a substrate illustrating anorganic EL device manufacture method according to the first embodiment.

FIG. 4A is a graph showing the characteristics of TFT of the organic ELdevice of the first embodiment, before and after ultraviolet radiation,and FIG. 4B is a graph showing the characteristics of TFT of aconventional organic EL device, before and after ultraviolet radiation.

FIG. 5 is a cross sectional view of the organic EL device of the secondembodiment.

FIG. 6 is a cross sectional view of a conventional organic EL device.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a cross sectional view of an organic EL device of the firstembodiment, and FIG. 2 is a plan view of one pixel.

As shown in FIG. 2, disposed on a substrate are a plurality of gatelines 2 extending in a row direction and a plurality of data lines 16extending in a column direction. The gate line 2 and data line 16 areelectrically insulated by an insulating film at an intersectiontherebetween.

A TFT 10 is disposed at each intersection between the gate line 2 anddata line 16. TFT 10 comprises first and second regions R1 and R2 as asource and a drain, and a gate electrode G. The gate electrode G isconnected to a corresponding gate line 2. The second region R2 isconnected to a corresponding data line 16.

A pixel electrode 25 is disposed in an area surrounded by two adjacentgate lines 2 and two adjacent data lines 16. The pixel electrode 25 isconnected to the first region R1 of a corresponding TFT 10. A cover film26 is disposed overlapping the outer periphery of the pixel electrode 25and covering the edge of the pixel electrode and an area having somewidth outside the outer periphery of the pixel electrode. The cover film26 covers the area superposing TFT 10, as viewed along a directionparallel to the normal direction of the substrate. The inner area otherthan the edge of the pixel electrode 25 is not covered with the coverfilm 26.

FIG. 1 is the cross sectional view taken along one-dot chain line A1-A1shown in FIG. 2. TFT 10 is formed on a silicon oxide film formed on aprincipal surface of the substrate. TFT 10 comprises a polysilicon film11 formed on the surface of the substrate 1, a gate insulating film I ofsilicon oxide 1 5 formed on the polysilicon film, and the gate electrodeG of AlNd alloy formed on the gate insulating film. A channel region Cis defined in the polysilicon film 11 in a region under the gateelectrode G, and n-type first and second regions R1 and R2 as a sourceand a drain are defined on both sides of the channel region. A thicknessof the polysilicon film 11 is 20 to 100 nm, a thickness of the gateinsulating film I is 100 to 150 nm, and a thickness of the gateelectrode G is 300 to 400 nm.

An insulating film 17 having a thickness of 300 to 500 nm is formed onthe substrate 1, covering TFT 10. The insulating film 17 is a singlelayer of silicon oxide or a multilayer of silicon oxide and siliconnitride. Via holes are formed through the insulating film 17 atpositions corresponding to the first and second regions R1 and R2 of TFT10. The data line 16 is formed on the insulating film 17. The data lineis made of a single layer of molybdenum (Mo) or a multilayer of titanium(Ti)/aluminum (Al)/molybdenum (Mo). The data line 16 is connected to thesecond region R2 of TFT 10 via the via hole formed through theinsulating film 17.

An intermediate connection metal 15 is formed on the surface of theinsulating film 17 in an area corresponding to the first region R1 ofTFT 10. The intermediate connection metal is made of a single layer ofmolybdenum (Mo) or a multilayer of titanium (Ti)/aluminum(Al)/molybdenum (Mo). The intermediate connection metal 15 is connectedto the first region via the via hole formed through the insulating film17.

An interlayer insulating film 20 is formed on the insulating film 17,covering the data line 16 and intermediate connection metal 15. Theinterlayer insulating film 20 is made of photosensitive resin (e.g.,acrylic resin) and its thickness is 3.0 μm. The interlayer insulatingfilm 20 has a planarized surface.

A via hole is formed in the interlayer insulating film 20, exposing theupper surface of the intermediate connection metal 15. A pixel electrode25 of ITO is formed on the surface of the interlayer insulating film 20.The pixel electrode 25 is connected to the intermediate connectionmember 15 via the via hole in the interlayer insulating film 20. Thepixel electrode 25 can therefore be electrically connected to the firstregion R1 of TFT 10 via the intermediate connection metal 15.

The cover film 26 disposed along the outer periphery of the pixelelectrode 25 covers the edge of the pixel electrode 25 and the uppersurface of the interlayer insulating film 20 in an area above TFT 10.The cover film 26 is made of photosensitive resist material, e.g.,novolak series resist material. An organic light emission layer 30 isformed on the surface of the pixel electrode 25.

For example, the organic light emission layer 30 has a four-layerstructure of a hole injection layer 30A, a hole transport layer 30B, alight emission layer 30C and an electron transport layer 30D stacked inthis order from the pixel electrode 25 side. The edge of the organiclight emission layer 30 extends to an upper surface portion of the coverfilm 26.

An upper electrode 35 covers the organic light emission layer 30 andcover film 26. The upper electrode 35 is made of aluminum and itsthickness is 100 to 200 nm. Voltage is applied across the pixelelectrode 25 and upper electrode 35, by using the pixel electrode 25 asan anode and the upper electrode 35 as a cathode. The cover film 26prevents a short circuit between the pixel electrode 25 and upperelectrode 35. As current is injected into the organic light emissionlayer 30, light is emitted. This light is radiated to the externalthrough the substrate 1.

Next, with reference to FIGS. 3A and 3B, description will be made on amanufacture method for the organic EL device of the first embodiment.

As shown in FIG. 3A, on the surface of a glass substrate such as #1737of Corning Limited, a silicon nitride film is deposited to a thicknessof 50 nm by plasma enhanced chemical vapor deposition (PECVD) to form asubstrate 1. On the silicon nitride film, a silicon oxide film isdeposited to a thickness of about 150 to 300 nm by PECVD. On the siliconoxide film, an amorphous silicon film is deposited by PECVD.

Heat treatment is performed at a temperature of 450° C. for one hour ina nitrogen atmosphere to degas hydrogen in the amorphous silicon film.The amorphous silicon film is polycrystallized by irradiating an excimerlaser beam having a wavelength of 308 nm. A pulse energy density of theradiated excimer laser beam is 300 to 400 mJ/cm². With this laserradiation, a polysilicon film 11 is formed. The polysilicon film 11 ispartially etched by reactive ion etching to leave the polysilicon film11 in an area where TFT is to be formed.

A silicon oxide film of 100 to 150 nm in thickness is formed coveringthe polysilicon film 11, by PECVD. On the silicon oxide film, an AlNdalloy film having a thickness of 300 to 400 nm is formed by sputtering.

By covering the surface of the AlNd alloy film with a resist pattern,the AlNd alloy film is wet-etched. By leaving the resist pattern, thesilicon oxide film under the AlNd alloy film is dry-etched by usingCHF₃. By leaving the resist pattern, the AlNd alloy film is laterallyetched to shrink the AlNd alloy film. In this manner, a gate insulatingfilm I of silicon oxide and a gate electrode G of AlNd alloy are formed.After the AlNd alloy film is side-etched, the resist pattern is removed.

By using a ion doping system, P⁺ ions are doped in PH₃ diluted gas of 1to 5%. In this case, first doping is performed under the conditions ofan acceleration energy of 10 keV and a dose of 5×10¹⁴ to 1×10¹⁵cm⁻², andsecond doping is performed under the conditions of an accelerationenergy of 70 keV and a dose of 5×10¹² to 5×10¹³cm⁻². An n-channel TFT ofa lightly doped drain structure (LDD structure) is therefore formed.

An insulating film 17 is formed on the substrate 1 by PECVD, coveringTFT 10. The insulating film is a multilayer of a silicon oxide film of50 nm in thickness and a silicon nitride film of 350 nm in thickness.Via holes are formed through the insulating film 17 at necessarypositions. An intermediate connection metal 15 and a data line 16 areformed by patterning a multilayer film of a titanium layer of 30 nm inthickness, an aluminum layer of 300 nm in thickness and a molybdenumlayer of 50 nm in thickness. An interlayer insulating film 20 ofphotosensitive resin (e.g., acrylic resin) is formed by spin coating,covering the intermediate connection metal 15 and data line 16. A viahole is formed in the interlayer insulating film 20 to expose the uppersurface of the intermediate connection metal 15.

An ITO film is deposited by sputtering and patterned to form a pixelelectrode 25. The pixel electrode 25 is connected to the intermediateconnection metal 15 via the via hole formed in the interlayer insulatingfilm 20.

As shown in FIG. 3B, a cover film 26 is formed by coating photosensitiveresist, exposing and developing it. The cover film 26 is superposed onthe outer periphery of the pixel electrode 25 and TFT 10, as viewedalong a line of view parallel to the normal of the substrate 1.

The substrate is placed in an ozone atmosphere and an ultraviolet ray isirradiated to the substrate surface on the side where the pixelelectrode 25 is formed, by using a low pressure mercury lamp. A mainwavelength of the radiated ultraviolet ray is 254 nm. An intensity ofthe ultraviolet ray at the substrate surface is about 6.7 mW/cm² and aradiation time is 20 minutes.

As shown in FIG. 1, an organic light emission layer 30 is formed on thepixel electrode 25 by vacuum vapor deposition using a shadow mask. Theorganic light emission layer 30 is made of a hole injection layer 30A, ahole transport layer 30B, a light emission layer 30C and an electrontransport layer 30D. An upper electrode 35 of aluminum is formed byvacuum vapor deposition.

The characteristics of the organic light emission layer 30 can beimproved by irradiating an ultraviolet ray to the surface of the pixelelectrode 25 of ITS in an ozone atmosphere, prior to depositing theorganic light emission layer 30. Similar advantages are expected for thecase that the pixel electrode 25 is formed by using transparentconductive material which contains indium.

In the above-described first embodiment, during the ultravioletradiation shown in FIG. 2, the intensity of the ultraviolet ray reachingTFT 10 is weakened because the cover film 26 shields the ultravioletray. It is therefore possible to prevent the characteristics of TFT 10from being degraded by ultraviolet radiation. The characteristics of TFT10 can be prevented from being degraded if the cover film 26 is disposedso as to be superposed at least upon the channel region C of TFT 10.

FIG. 4A shows the relation between a gate voltage and a source-draincurrent of TFT 10. The abscissa represents a gate voltage in the unit of“V” and the ordinate represents a source-drain current in the unit of“A”. A black circle in FIG. 4A indicates the characteristics beforeultraviolet radiation and a white circle indicates the characteristicsafter ultraviolet radiation. For the purposes of comparison, thecharacteristics of TFT are shown in FIG. 4B when ultraviolet radiationis performed without light shielding by the cover film 26. A blackcircle in FIG. 4B indicates the characteristics before ultravioletradiation and a white circle indicates the characteristics afterultraviolet radiation.

If TFT is not shielded with the cover film, it can be seen from FIG. 4Bthat the threshold value drifts and an on-current lowers, due toultraviolet radiation. In contrast, as in the first embodiment, since anultraviolet ray incident upon TFT 10 is shielded with the cover film 26,a threshold value drift and a lowered on-current are not observed.

In order to obtain sufficient effects of preventing the characteristicsof TFT 10 from being degraded, it is preferable to set an ultraviolettransmissivity of the cover film 26 to 30% or lower. For example, if alow pressure mercury lamp is used as an ultraviolet source, it ispreferable to set the transmissivity of the cover film to 30% or lowerat a wavelength of 254 nm.

In the first embodiment, although the ultraviolet radiation is performedin the ozone atmosphere, it may be performed in an oxidizing atmosphereother than ozone.

FIG. 5 is a cross sectional view of an organic EL device according tothe second embodiment. In the first embodiment, the cover film 26covering the edge of the pixel electrode 25 is extended to the areaabove TFT 10 and a portion of the cover film 26 is used as a lightshielding film. In the second embodiment, a cover film 26 only coversthe edge of a pixel electrode 25 and is not extended to the area aboveTFT 10. Instead, the area above TFT 10 is covered with a light shieldingfilm 36 made of metal, e.g., aluminum. For example, the light shieldingfilm 36 can be formed by lift-off.

In the second embodiment, although a new process of forming the lightshielding film 36 is necessary as opposed to the first embodiment, thetransmissivity of an ultraviolet ray can be lowered further by formingthe light shielding film 36 by using metal more likely to shield anultraviolet ray.

The present invention has been described in connection with thepreferred embodiments. The invention is not limited only to the aboveembodiments. For example, it will be apparent to those skilled in theart that other various modifications, improvements, combinations, andthe like can be made.

1. An organic EL device comprising: a thin film transistor formed on asubstrate, including a first region and a second region as a source anda drain, a channel region between the first and second regions, and agate electrode; an interlayer insulating film disposed on the substrate,covering the thin film transistor; a pixel electrode disposed on theinterlayer insulating film and electrically connected to the firstregion of the thin film transistor via a via hole formed in theinterlayer insulating film; a cover film covering an edge of the pixelelectrode and not covering an inner area of a surface of the pixelelectrode; a light shielding film for shielding an ultraviolet ray, thelight shielding film covering a surface of the interlayer insulatingfilm in an area superposed upon the channel region of the thin filmtransistor; an organic light emission film disposed on the pixelelectrode and containing organic light emission material; and an upperelectrode disposed on the organic light emission layer.
 2. An organic ELdevice according to claim 1, wherein the cover film and the lightshielding film consist of one layer made of same material.
 3. An organicEL device according to claim 2, wherein the cover film and the lightshielding film are made of photosensitive resist material.
 4. An organicEL device according to claim 1, wherein the pixel electrode is made oftransparent conductive material which contains indium.
 5. An organic ELdevice according to claim 2, wherein the pixel electrode is made oftransparent conductive material which contains indium.
 6. An organic ELdevice according to claim 3, wherein the pixel electrode is made oftransparent conductive material which contains indium.
 7. A manufacturemethod for an organic EL device comprising steps of: forming a thin filmtransistor on a principal surface of a substrate, the thin filmtransistor including first and second regions as a source and a drain, achannel region between the first and second regions and a gateelectrode; forming an interlayer insulating film over the substrate, theinterlayer insulating film covering the thin film transistor; forming apixel electrode disposed on the interlayer insulating film, the pixelelectrode being electrically connected to the first region of the thinfilm transistor; forming a cover film covering an edge of the pixelelectrode, exposing an inner area of a surface of the pixel electrode,and covering a surface of the interlayer insulating film in an areasuperposed upon the channel region of the thin film transistor;irradiating an ultraviolet ray upon the substrate from a principalsurface side of the substrate, while a surface of the pixel electrode isexposed to an oxidizing atmosphere; forming an organic light emissionfilm on the pixel electrode, the organic light emission film containingorganic light emission material; and forming an upper electrode on theorganic light emission layer.
 8. A manufacture method for an organic ELdevice according to claim 7, wherein a transmissivity of the ultravioletray passing through the cover film is 30% or lower.
 9. A manufacturemethod for an organic EL device according to claim 7, wherein the stepof forming the cover film comprises steps of: forming a resist film bycoating photosensitive resist on a surface of the interlayer insulatingfilm; and partially exposing and developing the resist film to form thecover film made of the remaining resist film.
 10. A manufacture methodfor an organic EL device according to claim 8, wherein the step offorming the cover film comprises steps of: forming a resist film bycoating photosensitive resist on a surface of the interlayer insulatingfilm; and partially exposing and developing the resist film to form thecover film made of the remaining resist film.
 11. A manufacture methodfor an organic EL device according to claim 7, wherein the pixelelectrode is made of transparent conductive material which containsindium.
 12. A manufacture method for an organic EL device according toclaim 8, wherein the pixel electrode is made of transparent conductivematerial which contains indium.
 13. A manufacture method for an organicEL device according to claim 9, wherein the pixel electrode is made oftransparent conductive material which contains indium.
 14. A manufacturemethod for an organic EL device according to claim 10, wherein the pixelelectrode is made of transparent conductive material which containsindium.